I am taking a trip to Hong Kong and want to stop in Beijing for 2 days on my way. Do i need a visa?

I plan on taking a trip to Hong Kong at the end of next month. I was wondering if it was possible to stop in Beijing for 2 days on my way to Hong Kong? Can I do it the 72 hours transit policy? I've spoken to Chinese Airlines and the Chinese embassy in Seoul and they don't know the right answer. I am a UK citizen living in Seoul.